1. Field of the Invention
The present invention relates to a method of controlling a continuously variable valve timing (hereafter, referred to as a “CVVT” for convenience) according to current control for an oil control valve (hereafter, referred to as an “OCV” for convenience) which can optimally control a CVVT by controlling current control for an OCV.
2. Description of Related Art
In general, internal combustion engines, apparatuses that generate power by receiving air and fuel from the outside and burning them in a combustion chamber, include an intake valve for sucking the air and fuel into the combustion chamber and an exhaust valve for discharging explosion gas burned in the combustion chamber, and the intake and exhaust valves are opened/closed by the rotation of a camshaft that rotates with rotation of a crankshaft.
It is required to make the timing of opening/closing the valves different in accordance with the degree of the engine speed or the degree of engine load, depending on the traveling conditions of a vehicle, in order to increase efficiency of the engine.
In particular, the timing of opening/closing the intake valve has a large influence on the charging efficiency, and when the intake valve is opened in advance, the valve overlap period increases and intake/exhaust inertia flow can be sufficiently used at a high speed, so the volume efficiency increases, but at a low speed, the volume efficiency decreases due to an increase in the amount of remaining gas and the discharge amount of HC (hydrocarbon) increases.
Therefore, the valve overlap period of the camshaft is not determined in accordance with the rotation of the camshaft and a technology of controlling an appropriate valve timing in accordance with the driving state of an engine for predetermined displacement has been used, and this is called a CVVT.
The CVVT is an apparatus (or system) that continuously changes the opening time of the intake and exhaust valves by changing the phase of the camshaft at the intake and exhaust sides in accordance with the load state of a vehicle and the engine speed, for example, that is, an apparatus that changes valve overlap and the object when to reduce exhaust gas, improve performance, and stabilize idling.
The valve timing means the timing where the intake valve and the exhaust valve open or close, the intake process is a process from opening to closing of the intake valve, the exhaust process of a process of discharging exhaust gas from opening to closing of the exhaust valve, and the timings of opening/closing the valves influence the performance of the engine.
The valve overlap means a period with both of the intake and exhaust valves open, and once the valve overlap is set in a common engine, it is constantly used throughout the section of the engine speed, such that it is disadvantageous at a low speed or high speed region.
Accordingly, controlling the valve overlap to fit to the engine load consequently improves the engine output and the part for the control fitting to the engine load is the CVVT.
The CVVT includes a continuously variable valve timing unit, an OCV that is an oil supply device, an OTS (Oil Temperature Sensor), an oil control valve filter and an oil passage, and an auto tensioner etc.
The continuously variable valve timing unit may be mounted on, for example, the camshaft at the exhaust side, the inside includes a housing and a rotor, an advance angle chamber and a retard angel chamber are provided between the housing and the rotor vane, and oil flows inside through the OCV, such that the rotor vane moves.
Further, the OCV is a core part of a CVVT apparatus and controls the valve opening/closing time by changing the passage of engine oil supplied from an oil pump and flowing to the continuously variable valve timing unit under the control of an ECU (Engine Control Unit).
The density of engine oil, which is a working fluid of the continuously variable valve timing unit, change in accordance with temperature and the OTS, a sensor that compensates for the amount of change according to temperature, measures the temperature before the engine oil flows into an OCV and sends it to the ECU and the ECU compensates for the change by driving the OCV.
Further, the oil valve control filter filters impurities in the engine oil flowing to the OCV and the oil tensioner, which is a tension control device of a chain connecting a sprocket of a camshaft at the exhaust side where the CVVT apparatus is disposed with a sprocket of the camshaft at the intake side, ensures stability of performance by preventing delay or deviation of responsiveness and problems in function of the CVVT apparatus.
As the CVVT apparatus, there is a D-CVVT (Dual Continuously Variable Valve Timing) apparatus that handles both of intake and exhaust valves, and since the intake valve moves only in the advance direction of the existing D-CVVT, there is a need of development for further improved optimal control and it is required to more optimally control a common CVVT apparatus too in accordance with the engine speed and load.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.